A communication system includes a collection of components that communicate, manipulate, and process information in a variety of ways. The system may support different access technologies, such as frame relay, circuit services, and new and evolving connection-based or connectionless services, that communicate information, such as data, voice, and video. Switches in the communication system employ hardware and software to route information generated by access technologies to an intended destination. In an integrated services network, switches may route information among access technologies in a unified manner.
One helpful way to think of a network is using the layering model such as the ISO model. In the ISO model, the communication problem is divided into subpieces or layers. The data link layer, layer 2, specifies how to organize data into frames and how to transmit frames over a network. The network layer, or layer 3, specifies how addresses are assigned and how packets are forwarded from one end of the network to another.
Multiprotocol Label Switching (MPLS) is a technique for improving the performance of networks by using layer 2 switching instead of layer 3 routing, independently of the routing scheme being used. The specification for MPLS is provided by the IETF (Internet Engineering Task Force).
MPLS uses labels or tags that contain forwarding information. These labels are attached to packets by the initial router, sometimes referred to as the ingress router or simply ingress. Switches and routers that receive the packets examine the label more quickly then if they had to look up destination addresses in a routing table. In this manner, communications can travel across the network more quickly.
MPLS is not specific to any type of network. Many initial commercial implementations, however, will focus on ATM (asynchronous transfer mode) networks since a large number of these networks have already been deployed throughout the world. Therefore, a need exists to adapt current ATM equipment to be compatible with MPLS.